1. Field of the Invention
The present invention generally relates to life-saving equipment used by swimmers and underwater breath-hold divers and, more particularly, to devices and apparatus for use by freedivers* to aid in returning them to the surface and/or maintaining them at the surface in the event of their losing consciousness due to hypoxia, a phenomenon often referred to among freedivers as “Shallow Water Blackout” (SWB). Without some form of rapid and immediate rescue effort, Shallow Water Blackout usually results in death. (*Freedivers are those individuals who venture underwater while holding their breath, and must therefore return to the surface to breathe.)
2. Description of the Related Art
Every year well-trained freedivers, who know the risks of Shallow Water Blackout (SWB), die at an alarming and almost predictable rate. All divers know to jettison their weight belts in an emergency situation. Yet, despite this knowledge, most SWB victims are found on the bottom with their (potentially) life saving weight belts still securely buckled in place.
The reasons behind this counterintuitive fact have been elusive. A recent global poll of freedivers revealed that the population of freedivers is greater than had been thought, and in conjunction, that deaths from SWB are greater as well.
Below is a table presenting the data gathered by this poll. As the data was collected and tallied, a trend began to emerge; that those who freedive in clearer waters are more apt to experience death from SWB.
COUNTRYFREEDIVERSSWB DEATHS/YEARUnited States- Continental10,0003United States- Hawaii5,0006Greece50,0006Australia15,00010 Italy12,50012 Portugal3,0003-5New Zealand1,0002South Africa8,5000-1France100,000-300,000 8-10**(In 2003,33 Frenchfreedivers diedfrom SWB)
The reason or reasons behind the all-to-frequent occurrence of SWB among experienced freedivers has, until recently, defied rational explanation. However, greater attention and careful scrutiny of the physiology and psychology of freedivers have yielded valuable insight.
Trained freedivers become adept at ignoring their desire to breathe. In addition, freedivers often are intensely focused and concentrating on a goal, be it depth, duration, or the pursuit of game. Add to this the hesitation experienced by many divers when faced with deciding whether to jettison their weight belt, and potentially ruin a day's diving, or to wait just a bit longer.
Through their having made thousands of successful freedives, some freedivers become over confident, especially under the influence of increasing hypoxia. One, some, or all of these factors can combine to cause a diver, who did not intend this freedive to be his last, to succumb to the often lethal effects of Shallow Water Blackout.
Human physiology changes day-by-day and minute-by-minute. What the experienced freediver has grown accustomed to as normal, may simply be beyond his/her ability to survive in special instances. In some cases, blackout occurs without warning. In other cases, the severely hypoxic freediver is incapable of operating his weight-belt quick-release mechanism. It is theorized that as the freediver approaches the end of a dive, there occurs a profound shift in their psychology, i.e., the freediver simply can no longer rely on their “internal clock” or whatever physiological/psychological mechanism it is that tells them it is time to ascend to safety. As a result, the freediver misperceives his remaining time underwater, and ventures unknowingly closer to unconsciousness due to SWB.
Shallow Water Blackout does not often come on gradually. Rather, the freediver often experiences a sudden “lights out”, and falls unconscious. Once unconscious, the opportunities for successful rescue diminish rapidly as minutes pass.
Others have attempted to reduce the risk of SWB through the use of inflatable belts, vests, or harnesses that could be inflated by a carbon-dioxide (CO2) filled cylinder in case of emergency. Some have gone so far as to connect a spring driven or mechanical timer to an inflatable buoyancy device. The timer would be activated by the freediver upon descent, and would count down during the dive. When the timer reached its end, it would activate the emergency inflation of the buoyancy device. Upon surfacing prior to the timed period elapsing, the freediver could reset the timer for the next dive, thereby providing some measure of protection against SWB.
These prior attempts have all incorporated mechanical timers of one form or another. Regardless of form, these timers were all relatively constant with regard to the timed period. That is, they possessed little, if any, ability to vary the period of time elapsed. And none presented the individual end user/freediver with the ability to easily and reliably customize the time interval to reflect their own capabilities.
Despite the immediate appeal of such devices, all they could do is provide the freediver with a false sense of security, in that all prior approaches to the problem of SWB have failed to realistically examine the variety of circumstances under which it occurs.
None of the prior devices address the fact that, once unconscious, the freediver frequently begins to sink into the depths. By the time a mechanical timer has run out, the freediver is often too deep for the CO2 cylinders to inflate the buoyancy device sufficiently to return the freediver to the surface. Boyle's law states that, for any gas at a constant temperature, the volume will vary inversely with the absolute pressure, while the density will very directly with the absolute pressure.
A simple application of Boyle's law to these circumstances reveals that, as a freediver descends underwater, the absolute pressure increases, and the volume of gas available for emergency release from a CO2 cylinder decreases. While the CO2 cylinder's volume might have been sufficient at the surface or near-surface depths, it often proves alarmingly incapable of lifting an unconscious freediver from depth.
In addition, while manual activation of an inflatable device is desirable in an emergency, all of the prior attempts have utilized CO2 cylinders, which are not refillable by the user. The not insignificant cost of these disposable cylinders raises the operating cost of the device, and thereby creates a disincentive for the freediver to deploy it. In addition, CO2 inflation devices are mechanical and are highly prone to corrosion problems. If the inflation device's cylinder cap piercing pin is allowed to become rusted, blunted, or if the CO2 pressure cap is unusually thick, these devices will not function properly in an emergency.